If Junior is overshadowed by Bowser, then Rosalina is overshadowed by Peach.
But this train of thought isn't important because Doctor Mario is DEFINITELY overshadowed by Mario, yet he still was playable. Rosalina just lacks a bit of everything IMO. (Don't get me wrong, I have a killer B moveset for her) Just, don't think she's going to happen, frankly.
And, I edited and quoted you on my last post splash ~